Translation:Early in the morning and late in the evening.
Actually I think it's better (easier?) to understand "wieczorem" as an adverb that just looks the same as Instrumental of 'wieczór'.
Or you can similarly use "rankiem" (from "ranek"), but "wcześnie rankiem" wouldn't work, you should also put it in Instrumental, "wczesnym rankiem".
That is a very good question. Short answer: It sort of works.
Wcześnie, rano, późno and wieczorem are all adverbs of time, which can't be preceded by an adjective. However, rano (nominative/accusative of rano=the morning) and wieczorem (instrumental of wieczór=the evening) can be interpreted as nouns as well. That's why you can use "późnym", which then automatically turns wieczorem into a noun.
It should work similarly for wcześnie rano, which would turn into wczesne rano. However, without the instrumental case, it just means "the early morning". That's why you need the instrumental case here as well: Wczesnym ranem, or perhaps more commonly wczesnym rankiem.
I'm not entirely sure whether mixing wcześnie rano (adverb+adverb) with póżnym wieczorem (adjective+noun) is stylistically acceptable. I'd have to ask.
Edit: Ok, so Jellei tells me that such a combination is not wrong per se, but perhaps not the best option, since it sounds a bit inconsistent.